Designing Shopify Custom Theme

Hi Indie Hackers! I'm a Ux/UI Designer and wanted to build my own Shopify Custom Theme to sell on my own site (TBD).

Does anyone have experience doing this?
Where do I start? (I'll be designing the screens in Figma)
Is there a library where it outlines in detail what I need to design? OR is it all code?

Would appreciate any guidance, and in return, I'm open to providing guidance on any of your Ux/UI needs.

Once I'm done with the layouts I'm planning on hiring a developer to build to Shopify's requirements.

Thanks!!